First, I don't think the answer that "All of the statements I made are from the mainstream explanations," is sufficient, because there are all sorts of incorrect "explanations" of things on the Internet. What I am asking for is what actual observations
support those "explanations."
With regard to radio antenna efficiency and "photon size", I will observe that I can both transmit and receive radio signals on antennas that are specific fractions of the tuned wavelength, namely 1/4, 1/2, 5/8 and 3/4. That is why I asked what the "size" of an inflated photon would be in terms of its wavelength, and included the possibility that the "dimensions" of a photon "particle" might be more or less
than its wavelenght parameter. There seems to be some difficulty reconciling that with the idea that the photon emitted by an electron jumping energy states in a hydrogen atom will not be absorbed in another hydrogen atom if there is any perterbation to its energy level at the absorption end, either by expanding space or having the two hydrogen atoms have a significant velocity difference. (Maybe a photon energy is the second Eigen value wavelength of something in the atomic structure, or what?)
Where we really got separated is in your statement:
I do not claim that photons are not stretched. Energy is conserved within any given reference frame. They are stretched in the moving observer's reference frame. Once received, the energy will be lower than normal. But in the emitting reference frame the photon never lost any energy. Two different reference frames, two different energies.
To get the motion aspect out of the discussion, consider that the hydrogen atom emits the photon, then space stretches and then stops stretching
and then the receiving antenna is at rest with respect to the hydrogen atom when the photon gets there. It is still "redshifted" by the stretching of space, but not by differential motion. That is what I want to discuss, with respect to conservation of energy, and you seem to agree that the energy of the photon should be the same for emission and adsorption in that case. (I do understand that the energy measurements are not conserved between two frames of reference that are in motion with respect to each other - as in you previous example of the kinetic energy of a bullet and its massive target from the perspectives of the frames of reference of the target and the bullet.)
In the example that I am trying to discuss, the frame of reference is the same for the emitter and the receiver at the times that the emission occurred and the absorption occurred. It is just a portion of the duration between those points in time that space gets stretched, and that did "something" to the photon in the process. That scenario is similar to what is postulated for the "Inflation period" of the BBT. Although in the BBT, the expansion is not assumed to actually be zero rate at any time, it is assumed to have mostly occurred in a tiny fraction of a second (10^-35 to 10^-32 second after the "Bang"). So, to make things simple, I want to do the thought experiment with the expansion rate at zero during emission and absorption, but total expansion be a factor of 2 m / 1.21567×10−7 m = 16,451,833 within some instant between the times of emission and absoption. That expansion factor is peanuts inflation compared to what the BBT assumes for the universe during the "Inflation period", so I don't see how BBT proponents could call a foul on that thinking.
So, my fundamental question is: What is that "something" that happens to a single
photon when it gets stretched by "inflation of space" from a quantum level entity to a marco level entity? It is easy to describe the effect in terms of waves, but how do we conceive it in terms of a single particle?